Optical device for viewing of cavernous and/or inaccessible spaces

ABSTRACT

An optical device for viewing an object at a range of working distances. The device comprises a slender tube of a certain length and having a distal end and a proximal end. The device farther comprises an imaging system disposed at the distal end and having a wide viewing angle. The device also comprises a telescopic system associated with the proximal end and having a narrow viewing angle. The imaging system is designed to form an image of the object at an image plane located on the device&#39;s optical axis and within the tube closer to the distal end than to the proximal end. The telescopic system is designed to enable viewing of the image of the object. The device is especially adapted to function as an endoscope in medical applications and may be disposable.

FIELD OF THE INVENTION

[0001] This invention relates to optical instruments adapted for viewingof cavernous and/or inaccessible spaces and which may be employed toview objects such as internal body organs and cavities thereof, as wellas particular objects located in such organs, e.g. a tumor or a cyst.These optical instruments include endoscopes, otoscopes, laparoscopes,arthroscopes, bronchoscopes, laringoscopes, cystoscopes and othersimilar rigid endoscopic medical examination devices. Such opticalinstruments are not limited to medical use, however, and may be found inany of a variety of fields in which inspection as described above may beapplicable, e.g. in mechanical applications, such as in the form of aborescope. More particularly, the invention relates to such opticalinstruments that are further designed to be disposable.

BACKGROUND OF THE INVENTION

[0002] Various optical instruments, which are designed to enable viewingof areas not easily accessible or directly available for inspection, areknown in the art. In medical applications, for example, a plurality ofoptical instruments, such as endoscopes, arthroscopes, bronchoscopes,and the like, are used for examining the interior of body cavitiesranging from ear canals to joints and lungs. Access to such cavities bythese instruments is typically achieved via a natural body conduitconstituting or leading to the cavity. In some cases, however, it isknown to make a small surgical incision by which the instrument may gainaccess to the cavity.

[0003] Rigid and flexible endoscopes are known in the art. Unlike theirrigid counterparts, flexible endoscopes allow access to considerablycavernous and distant areas of the body, such as the intestinal tract.However, when compared with rigid endoscopes, flexible endoscopesprovide reduced image quality, are relatively expensive, and are notsuitable for many applications. They are also normally not adapted towithstand sterilization by an autoclave.

[0004] Rigid endoscopes have advantages in the above respects,particularly as far as image quality is concerned. In general, a rigidendoscope comprises an elongated tube having a distal end for insertioninto a body cavity, a proximal end with an eyepiece, and a plurality oflenses located inside the tube and along its length for forming an imageof the body cavity, and/or objects located therein, and transferring theimage to a viewing component, by which it may be viewed e.g. by aphysician. Typically, the interior surface of the tube is black coatedin order to prevent undesirable residual light reflections therein.

[0005] U.S. Pat. No. 5,891,015 discloses an endoscope comprising a rigidtube having a distal end, a proximal end with a viewing componentincluding an image-sensitive surface, and an imaging systemtherebetween, which fully occupies the tube's interior and includes asingle ashperical planar-concave front lens, a single aspherical innerlens, and two glass rods. The imaging system serves to form an image ofthe object and to subsequently relay it to the image-sensitive surface,which reads the image and enables it to be displayed for viewing.

[0006] U.S. Pat. No. 6,398,724 discloses an endoscope including a sealedinsertion tube with a distal end and a proximal end, which is associatedwith a focusing assembly having optical components and being mounted inan endoscope housing to which the tube is detachably attachable. Theinsertion tube comprises optical elements located therein along itslength and adapted to form an image of the object inside the focusingassembly, wherefrom the image is transferred by the optical componentsto an image plane coinciding with the image-sensitive surface of a CCDsensor. The image of the object may be focused by moving the CCD sensorso as to adjust the distance between the image-sensitive surface and thestationary image. The detachable insertion tube is autoclavable, and maytherefore be sterilized alone, thereby eliminating the need to sterilizethe entire endoscope, especially components thereof, such as thefocusing assembly and the CCD sensor, whose adequate sterilization isconsiderably more complex and costly.

[0007] It is crucial for reuseable medical instruments to be sterilizedbefore their reuse, and such sterilization is performed by variousmethods, such as by autoclaving. However, the delicate and complicatedconstruction of reuseable endoscopes makes their absolute sterilizationdifficult to achieve.

[0008] Accordingly, a need in the art has developed for a disposableendoscope, which on the one hand, provides high quality imaging, whileon the other, may be produced from relatively inexpensive components andmanufactured sufficiently inexpensively as to be cost-effective fordisposal after single-patient use.

[0009] Attempts to design disposable endoscopes are known anddisclosures thereof include, for example, U.S. Pat. Nos. 4,964,710,5,188,092, and 5,892,630.

SUMMARY OF THE INVENTION

[0010] The present invention suggests an optical device for viewing anobject at a range of working distances, the device having an opticalaxis and comprising a slender tube of a certain length and having adistal end and a proximal end, an imaging system disposed at said distalend and having a wide viewing angle, and a telescopic system associatedwith said proximal end and having a narrow viewing angle, the imagingsystem being designed to form an image of said object at an image planelocated along said axis and within said tube closer to the distal endthan to the proximal end, the telescopic system being designed to enableviewing of said image of the object.

[0011] Being associated with the proximal end of the slender tube thetelescopic system of the optical device in accordance with the presentinvention is spaced from the imaging system and the image plane by amajority of the length of the slender tube which length is chosendepending on the intended application for which the device is designed.However, for any chosen length, the viewing angle of the telescopicsystem is always so narrow as to span no more than the slender tube'swidth at the location of the image plane. In this way, the telescopicsystem enables viewing of the image of the object without a need forintermediating image-forming optical components, such as a plurality ofrelay lenses within the tube to transfer the image to the proximal endof the tube.

[0012] The wide viewing angle of the imaging system of the opticaldevice according to the present invention may be as in conventionaloptical devices of the kind to which the present invention refers.Preferably, however, this viewing angle is so wide and, consequently,the imaging system possesses such a short focal length that the locationof the image plane lies within the depth of field of the telescopicsystem over the entire range of working distances. Thus, the telescopingsystem may be fixed in a predetermined disposition, enabling the opticaldevice to provide a clear view of the image of any object located withinthe working range, without requiring adjustment of the telescopicsystem.

[0013] To achieve the simplest and most inexpensive design possible forthe optical device in accordance with the present invention, the imagingsystem possesses a minimum number of elements necessary to provide itswide viewing angle, with all of these elements being concentrated at thedistal end of the tube. To this end, the imaging system preferablyincludes a single element in the form of a whole ball (i.e. a sphere)lens, which may have certain sections removed therefrom, e.g. an outercylindrical portion of the sphere cut therefrom to yield a drum-likeshape. The use of a ball lens is preferred not merely because such alens possesses the shortest focal length possible for a single element,but also since it provides an added advantage of producing relativelylittle chromatic aberration and causing a negligible amount ofdistortions such as astigmatism and coma. Furthermore, geometricdistortions produced by the ball lens may be easily calculated and maytherefore also be easily corrected either by image processing techniquesor optically, such as by incorporation of corrective optics. Suchcorrective optics preferably consists of a single corrective opticalelement adapted to reduce the distortions of the imaging system. Thecorrective optical element may be in any suitable form, such as that ofa plano-convex lens, capable of achieving this end.

[0014] The imaging system of the optical device according to the presentinvention may alternatively contain an aspherical, wide viewing anglemember having many of the desirable features of the ball lens butproducing considerably less distortion, preferably to the extent that acorrective optical element would be unnecessary.

[0015] The imaging system may further include illumination light guidesurrounding the circumference of the tube, which may be in any formknown in the art, e.g. in the form of fiber optic strands or of anannular cylinder, extending along the tube.

[0016] Viewing of the image of the object by use of the optical deviceof the present invention may be achieved directly with the human eye orindirectly therewith, such as via means for relaying the image to animage-sensitive device such as a video image sensor, photographic film,and the like, after which it may be displayed, e.g. on video screen.

[0017] One of the most essential applications of the optical device ofthe present invention is its use as an endoscope, in which case theslender tube is preferably rigid and may have any dimensions adapted forthe intended application of the endoscope so long as the tube's totallength is considerably greater than its width, with the majority of thetube being free of optical elements, since, as mentioned above,components of the imaging system are concentrated at the distal end andthe telescopic system is associated with the proximal end of the tube.For example, for an imaging system including a ball lens, as mentionedabove, having a diameter d, the entire imaging system is typicallyspread within the tube over a single continuous length of but about 2-3times the diameter d, while the tube's total length spans about 10-100times the diameter d.

[0018] The present invention affords a simple design of an endoscope incomparison to many of those known in the art as it can operate with buta few optical elements, most of which are positioned at one of twolocations i.e. near the distal end of the slender tube as part of theimaging system or near the proximal end as part of the telescopicsystem. Thus, the simple design of the endoscope of the presentinvention affords the device a number of considerable advantagesincluding the device's relatively low sensitivity to bending forces andother mechanical loads that may be applied thereto during handling, whencompared with relatively complicated endoscopic designs known in the arthaving many lenses and/or other optical elements, which have a tendencyto render the endoscope optically inoperable even after slight bending,and often become damaged thereby. Furthermore, the endoscope of thepresent invention is easily assembled, especially because its limitednumber of image-forming optical components is located at few andspecific locations of the device, specifically near its extremities.

[0019] In addition to the foregoing, the simple design of the presentinvention provides yet another advantage in the ability to thus producea relatively inexpensive endoscope or other such device, which therebyalso enables production of a completely disposable endoscope or of onehaving disposable parts, such as the rigid slender tube with its imagingsystem. Such an endoscope tube is, in fact, another aspect of thepresent invention.

[0020] The facility with which the endoscope or the endoscope tube ofthe present invention may be rendered sufficiently inexpensive to bedisposable is a particularly beneficial feature in medical applicationswhere instruments for introduction into the human body, for example,must often undergo sterilization.

[0021] Also, the simple design and assembly of the endoscope inaccordance with the present invention enables its cost to besufficiently minimized, particularly by choosing less expensivematerials and methods for its manufacture, for example, that it maybecome economically feasible to dispose of the endoscope in its entiretyafter each use thereof. For example, the cost of the endoscope may beminimized by producing the imaging system, the telescopic system, theslender tube, as well as other parts of the endoscope body, fromsuitable plastic materials. In addition, the use of a ball lens in theimaging system, as mentioned above, for example, may be especiallyadvantageous in this respect since, due to its simple geometry, the balllens may be easily and inexpensively produced. Furthermore, due to itssymmetry, the ball lens is easy to assemble, as its orientation isidentical in any disposition.

[0022] Another example of a preferred manufacturing method includesproduction of the slender tube from a strip of metal sheeting which isblacked on one side by galvanic coating, paint, or other suitablematerial. The strip is then cold or hot drawn and welded to form thetube, with the blackened side constituting its inner surface to serve asa means, as known in the art, for preventing unwanted residualreflections of light from propagating through the tube and adverselyaffecting the image quality.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to understand the invention and to see how it may becarried out in practice, different embodiments will now be described, byway of non-limiting example only, with reference to the accompanyingdrawings, in which:

[0024]FIG. 1 is a schematic illustration of an optical set-up of anendoscope according to the present invention;

[0025]FIG. 2 is a schematic partial cross-sectional view of oneembodiment of the endoscope illustrated in FIG. 1;

[0026]FIG. 3 is an enlarged cross-sectional view of a portion of theendoscope, designated as III in FIG. 2;

[0027]FIG. 4 is a schematic partial cross-sectional view of anotherembodiment of the endoscope illustrated in FIG. 1;

[0028]FIG. 5 is an enlarged cross-sectional view of a portion of theendoscopes, designated as V in FIGS. 5 and 7;

[0029]FIG. 6 is a schematic cross-sectional view of a portion of theendoscopes, designated as VI in FIGS. 5 and 7; and

[0030]FIG. 7 is a schematic partial cross-sectional view of yet anotherembodiment of the endoscope illustrated in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

[0031] An endoscope 2 in accordance with the present invention isgenerally described below with reference to FIG. 1. The endoscope 2 isadapted for viewing, by a viewer's eye E or an image-receiving viewingdevice e.g. a CCD camera (not shown), an object 3, such as an interiorof a body organ or a tumor, within a pre-determined range of workingdistances. The endoscope 2 comprises an imaging portion 2 a and aviewing portion 2 b arranged along a common optical axis ο.

[0032] The imaging portion 2 a includes a hollow rigid slender tube 4with an imaging system 8 mounted therein. The slender tube 4 has a widthw and a length L separating its distal end 5 and proximal end 6, thelength L being considerably greater than the width w of the tube. Theimaging system 8 is disposed within the tube 4 near its distal end 5 andis adapted to form an image of the object 3 on image plane 9 locatedadjacent to the imaging system 8. The imaging system 8 possesses such awide viewing angle α, i.e. a short focal length, that the location ofthe image plane 9 varies only slightly in response to changes in theworking distance. To provide the indicated wide viewing angle, theimaging system 8 comprises, for example, a single ball lens 12 ofdiameter d and a corrective optical element in the form of aplano-convex lens 13 adapted to reduce distortions produced by the balllens 12. The imaging portion 2 a further comprises a window 7 at thedistal end 5 of the tube 4 in front of the ball lens 12.

[0033] The viewing portion 2 b of the endoscope 2 includes a housing 11to which the tube 4 is connected at its proximal end 6, and a telescopicsystem 10 accommodated within the housing 11. The telescopic system 10comprises a first converging lens 20 and a second converging lens 22,thereby defining a Newtonian telescope arrangement. The telescopicsystem 10 possesses a narrow viewing angle β defined by the width w ofthe tube 4 and a distance between the image plane 9 and the firstconverging lens 20. Due to such a narrow viewing angle, and in view ofthe fact that the optical elements (i.e. the lenses 12 and 13) of theimaging system 8 are concentrated at the distal end 5 of the tube 4 andthose (i.e. the lenses 20 and 22) of the telescopic system 10 are nearthe proximal end 6 of the tube 4, the majority of its length L is freeof optical elements, especially between the image plane 9 and thetelescopic system 10. Thus, for example, with the length L of the tube 4being about 10-100 times the diameter d of the ball lens 12, and theimaging system 8 spanning a length of about 2-3 times the diameter d,about 70-98% of the length of the tube remains free of optical elements.

[0034] The telescopic system 10 has a pre-determined depth of field andit is so spaced from the imaging system 8 as to ensure that the imageplane 9, whose position varies only slightly with variation in theworking distance due to the wide viewing angle of the imaging system,lies within the depth of field over the entire range of workingdistances. Thus, the telescoping system 10 may be fixed in apredetermined arrangement, while still enabling the endoscope 2 toprovide a clear view of the image of any object located within the rangeof working distances, thus eliminating a necessity for adjustment of thetelescopic system 10.

[0035] The telescopic system 10 is designed to have magnificationparameters such as to ensure that the image of the object 3 formed atthe image plane 9 and viewed through the telescopic system, fullyoccupies the active part of the retina of the viewer's eye E or animage-sensitive surface of another image-receiving viewing device e.g. aCCD sensor. In this way, the telescopic system 10 enables viewing of theimage of the object without a need for any intermediating components,such as a plurality of lenses within the tube, to transfer the image tothe proximal end 6.

[0036] In operation, light rays reflected off the object 3 and enteringthe endoscope 2 through the window 7 along the optical axis ο areconverged by the ball lens 12 and the plano-convex lens 13 and an image(not shown) of the object 3 is formed at the image plane 9. Thetelescopic system 10 transfers the image from the image plane 9 to theviewer's eye E. As the working distance between the object 3 and theendoscope 2 changes, the location of the image plane 9 changesaccordingly. Due to the very short focal length of the ball lens 12,however, the position of the image plane 9 is changed to such a slightextent that even for considerable changes in working distance, thetelescoping system 10 will still enable clear viewing of the object'simage. Therefore, the telescoping system 10 does not require adjustmentdespite variation in working distance.

[0037] The above-described operation of the endoscope according to thepresent invention has been modeled and tested by computerizedsimulations using commercially available ray-tracing programs and bytheoretical calculations based thereon. In addition, test models of theendoscope have also been built, two examples of which are presented, forexample, below. ENDOSCOPE PARAMETERS Model 1 Model 2 1. Length L of thetube 4 110 180 2. Range of working distances, mm 3-∞ 3-∞ 3. Width w ofthe tube, mm 3 3 4. Viewing angle of the imaging system (FOV), ° 70 705. Focal length of the ball lens, mm 2.2 2.2 6. Diameter d of the balllens, mm 3 3 7. Diameter of the corrective element, mm 3 3 8.Magnification of the telescopic system 5 7 9. Optical power ofcorrective element, diopters 100 100 10. Optical power of telescopicsystem's first lens, 25 25 diopters 11. Optical power of telescopicsystem's second 125 167 lens, diopters 12. Depth of field of thetelescopic system, mm 1.4 1.4 13. Range of locations of the image plane(over the 1.4 1.4 entire range of working distances), mm

[0038] FIGS. 2 to 7 show three different embodiments of the endoscope ofthe present invention all based on the optical set-up and conceptdescribed above and shown in FIG. 1. In particular, each of theendoscopes includes an endoscope tube with the imaging system 8 at itsdistal end, and an endoscope housing receiving the proximal end of thetube and accommodating therein the telescopic system shown in FIG. 1.The endoscopes shown in FIGS. 2 to 7 all have illumination light guidemeans extending along the tubes from a location close to their proximalends to their distal ends, for illuminating an object to be imaged. Theillumination light guide means in the endoscopes include connectorsmounted to the endoscope housing, which are connectable with a lightguide of a light source (not shown).

[0039]FIG. 2 shows a reusable endoscope 102 including an endoscope tube104 and housing 111 permanently coupled therewith. The tube 104 includesspaced apart internal sleeve 142 and external sleeve 144, and theendoscope comprises illumination light guide means in the form of fiberoptics strands 140 which extend between the internal and externalsleeves 142 and 144 of the tube 104 and through the housing 111 so as toenable communication with a light source via a connector 150, as knownin the art.

[0040]FIG. 3 shows an enlarged view of the distal end of the endoscope102 shown in FIG. 2, illustrating the simple manner by which the lenses12 and 13 are mounted in the internal sleeve 142 of the tube 104together with spacers 160 therebetween, which serve to fix the lenses ina predetermined operational disposition.

[0041]FIG. 4 shows an endoscope 202 having a disposable endoscope tube204, with its internal sleeve 142 containing the imaging system 8 as inthe endoscope 102 described above and being devoid of an externalsleeve. The endoscope 202 further includes a reusable endoscope housing211, and the tube 204, detachably connected thereto. The illuminationlight guide means are in the form of an annular light guide cylinder 218coaxially and contiguously adjoining the internal sleeve 142 to channellight from a light source via a connector 250 mounted in the housing211.

[0042]FIG. 5 shows an enlarged view of the distal end of the endoscope202 shown in FIG. 4, illustrating the light guide cylinder 218 extendingalong the internal sleeve 142 and having a bulged extremity 270 at thedistal end of the tube 204.

[0043] The light guide cylinder 218 may be formed from a transparentmaterial and have inner and outer surfaces coated with a material whoseindex of refraction is lower than that of the light guide material. Thecylinder 218 is thus able to conduct light based on the principle oftotal internal reflection. Alternatively, the cylinder 218 may be coatedon its outer and inner surfaces by a reflective coating, thereby alsoenabling it to efficiently channel light therethough. Various types oflight guide cylinders are known in the art, and their means ofconnection to the connector 250 (shown in FIG. 4) may be learnedtherefrom, e.g. from U.S. Pat. Nos. 5,396,366 and 5,423,312.

[0044] The light guide cylinder 218 of the endoscope 202 according tothe present invention is especially advantageous in comparison to afiber optic arrangement, such as that described above with reference toFIGS. 2 and 3, in that it is considerably less expensive to produce andassemble. This allows the tube 204 to be made cost-effectivelydisposable, especially if the cylinder 218 as well as the imaging system8 and the tube 204 itself are made from suitable low-cost materials andhave easy-to-assemble design. In this way, the tube 204, including theimaging system 8 and the light guide cylinder 218, may be manufacturedseparately and detachably joined to the endoscope 202, so that it may bedisjoined after use, disposed of, and replaced by another new such tube.Furthermore, the cylinder 218 is capable of transmitting more light thanthe arrangement of fiber optic strands 140 shown in FIGS. 2 and 3. Thelatter is due to the fact that spaces unavoidably existent betweencylindrical fiber optic strands are, in the case of the cylinder 218,occupied by the material of the cylinder 218, which is also able tocontribute to the amount of projected light.

[0045] To provide yet another advantage, during its manufacture, theextremity 270 of the light guide cylinder 218 is thermally processed tohave the shape of a spherical bulge so as to enable light to bedistributed therefrom at a relatively wide angle. Similarly, theextremity of the cylinder 218 in the endoscope of the present inventionmay be made, by any known methods, to have a wide variety of otherdesigns adapted to direct the light projected therefrom in a desiredintensity distribution to suit the viewing angle of the imaging system.

[0046] As shown in FIG. 6, the endoscope 202 (shown in FIGS. 4 and 5)has an L-shaped connecting light guide element 280, disposed on theinternal sleeve 142 of the tube near its proximal end following thelight guide cylinder 218 and extending into the connector 250. Theelement 280, which is annular in the region near its first end 280 a butsolid in the region adjacent its second end (not shown), is adapted toconduct light, at its second end, from the light guide means of thelight source and channel it to the light guide cylinder 218, which itabuts at the first end 280 a. The element 280 has a specific designdirected to maximizing light transmission efficiency as itscross-sectional area at the first end 280 a matches that of the cylinder218, while tapering within the connector 250 near second end to matchthat of the light guide means of the light source. In this way, theelement 280 serves to enable light to be conducted from the light sourceto the cylinder 218 with minimal loss of light therebetween.

[0047]FIG. 7 shows the endoscope 302, which is similar to the endoscope202 of FIGS. 4-6 in the design of its tube 304, its light guide cylinder218, and its light guide element 280, and differing only in that it isdesigned to be disposed of in its entirety following each use, i.e. itshousing 311 with its telescopic system (shown in FIG. 1) accommodatedtherein is also disposable. The tube 304 may be integral or detachablyconnectable to the housing 311.

[0048] It should be understood that the above-described endoscopes areonly examples of an optical device in accordance with the presentinvention and that the scope of the present invention fully encompassesother embodiments and applications that may become obvious to thoseskilled in the art. Thus, the optical device may be directed to enableviewing of any areas not easily accessible or directly available forinspection. As the device is particularly useful in a wide variety ofmedical fields where inspecting the confines of cavernous regions of apatient may be desired, the optical device may not only be used as anendoscope, but may be a part of any similar instrument including anotoscope, laparoscope, arthroscope, bronchoscope, laringoscope,cystoscope or other such endoscopic medical examination device, mutatismutandis. Furthermore, while the present description focuses on theembodiment of the optical device of the present invention as anendoscope and the like, it should be noted that the device is notlimited to medical use and may be employed in any of a variety of fieldsin which inspection as described above may be applicable, e.g. inmechanical applications such as in the form of a borescope, mutatismutandis. In fact, the endoscopes shown in FIGS. 2-7 may also be used asborescopes.

[0049] In addition, the optical device described above may haveadditional components such as, for example, various light-deflectingelements (e.g. prisms), as known in the art, which, along with all othercomponents of the imaging system, can be positioned at the distal end toenable viewing of objects distanced from the optical axis. For thispurpose, the ball lens may have portions cut therefrom, as mentionedabove, to give it a front frusto-conical shape so as to free up space toaccommodate such elements.

[0050] Also, the endoscope may comprise a front window heating mechanismadapted to prevent vapor from condensing on the window's surface. Theendoscopes' connectors 150 and 250 to the light source may also bepositioned at other locations, e.g. at the far end of the housingopposite the distal end of the tube so as to be a hindrance duringmedical examinations and the like.

1. An optical device for viewing an object at a range of workingdistances, the device having an optical axis and comprising a slendertube of a certain length and having a distal end and a proximal end, animaging system disposed at said distal end and having a wide viewingangle, and a telescopic system associated with said proximal end andhaving a narrow viewing angle, the imaging system being designed to forman image of said object at an image plane located on said axis andwithin said tube closer to the distal end than to the proximal end, thetelescopic system being designed to enable viewing of said image of theobject.
 2. An optical device according to claim 1, wherein saidtelescopic system is spaced from said image plane by a majority of saidlength.
 3. An optical device according to claim 2, wherein said narrowviewing angle is defined by a width of the tube at the location of theimage plane and a distance between the image plane and the telescopicsystem.
 4. An optical device according to claim 1, wherein said viewingangle of the imaging system is so wide and, consequently, its focallength is so short that said location of the image plane lies within thedepth of field of the telescopic system over the entire range of workingdistances.
 5. An optical device according to claim 1, wherein theimaging system includes at least one imaging element having said wideviewing angle and at least one corrective optical element adapted toreduce distortions in said image resulting from said imaging element. 6.An optical device according to claim 5, wherein said imaging elementincludes a ball lens.
 7. An optical device according to claim 5, whereinthe corrective optical element is a plano-convex lens.
 8. An opticaldevice according to claim 6, wherein the ball lens has a diameter d andthe imaging system is spread within the tube over a single continuouslength of about 2-3 times the diameter d, with the tube's lengthspanning about 10-100 times the diameter d.
 9. An optical deviceaccording to claim 1, wherein the device is designed to be completelydisposable.
 10. An optical device according to claim 1, wherein at leastone optical component of the imaging system or the telescopic system ismade from plastic.
 11. An optical device according to claim 1,comprising a reusable section including said telescopic system, and adisposable section in the form of said tube detachably mountable to saidreusable section.
 12. An optical device according to claim 1, whereinthe device is an endoscope.
 13. An optical device according to claim 1,wherein the device is a borescope.
 14. An optical device according toclaim 1, further including an illumination light guide designed tocoaxially and contiguously adjoin said slender tube.
 15. An opticaldevice according to claim 14, wherein said light guide is composed offiber optic strands.
 16. An optical device according to claim 14,wherein said light guide is an annular cylinder.
 17. An optical deviceaccording to claim 16, wherein said annular cylinder has an extremityprocessed to have a design adapted to direct the light projectedtherefrom in a desired intensity distribution suited to the viewingangle of the imaging system.
 18. An optical device according to claim16, further including a light guide element adapted to conduct lightfrom a light source to the cylinder, the element being designed to matchthe cylinder at one end and to match the light source at the other endso as to reduce loss of light.
 19. A slender tube for use with theoptical device defined in claim 1.